<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div>index.html</div>
    <script>
        var div = document.querySelector('div')
        div.style.width = '200px'
        div.style.height = '200px'
    </script>
    <style>
        div {
            color: brown;
            font-size: 30px;
            background-color: bisque;
        }
    </style>
</body>

</html>